1. Field of the Invention
The present invention relates to the field of carrier aggregation in a wireless communication system. More particularly, the present invention relates to an apparatus and method for activating and deactivating secondary cells in a carrier aggregation environment.
2. Description of the Related Art
Wireless communication systems are widely deployed to provide various communication services such as voice, video, packet data, broadcast, messaging, and so on. These systems may be multiple-access systems capable of supporting communication for multiple users by sharing the available system resources.
Recently, in wireless communication technologies such as Long Term Evolution (LTE)/LTE-Advanced (LTE-A), carrier aggregation has been introduced such that two or more component carriers are aggregated in order to support wider transmission bandwidths of up to 100 MHz. More specifically, carrier aggregation enables a User Equipment (UE) to aggregate a different number of cells comprising component carriers and different bandwidths in both uplink and downlink.
Typically, in a carrier aggregation environment, a UE can have more than one cell for data communication. In such a situation, one cell is a Primary cell (Pcell) and the remaining cells are Secondary cells (Scells). Both the Pcell and the Scells may have a downlink component carrier and an uplink component carrier. At any given time, the LTE network can add or remove one or more Scells to the UE based on data requirements. Similarly, the LTE network can activate one or more configured Scells from a deactivated state and vice versa based on data requirements. For example, an Scell configured for the UE is deactivated from the activated state due to non-use of the configured Scell for data communication as the unused Scell may consume a significant amount of battery power of the UE. The deactivated Scell may not be involved in any active data communication.
Typically, an enhanced-NodeB (eNB) communicates activation/deactivation of one or more S cells configured for use by the UE using a Medium Access Control (MAC) Control Element (CE) command. Thus, the UE activates/deactivates the one or more Scells upon receiving the MAC CE command from the eNB. When the MAC CE command is received by the UE, the UE sends a positive/negative acknowledgment (ACK/NACK). Usually, a Physical Uplink Control Channel (PUCCH) is used for transmission of ACK/NACK. However, when an uplink grant is available, ACK/NACK is sent over a Physical Uplink Shared Channel (PUSCH) since the PUSCH provides better transmission reliability as compared to the PUCCH.
If the eNB does not receive the ACK/NACK due to reliability issues, the eNB may consider that the UE has not received the MAC CE command. However, if the UE does receive the MAC CE command, the state of one or more S cells may remain unsynchronized between the UE and the eNB. For example, the eNB may transmit a MAC CE command for activating an Scell that is received by the UE, but the corresponding ACK/NACK may not be received by eNB. In such case, the eNB may incorrectly assume that the Scell is not activated at the UE due to failure to receive the ACK/NACK. This may result in significant loss of power at the UE. Similarly, if the MAC CE command is for deactivation of an Scell, the eNB may assume that the S cell is not deactivated at the UE even though the UE has deactivated the Scell, thereby causing a waste of network resources and scheduling errors. That is, the eNB is not sure of whether the UE has successfully received the MAC CE command for activating/deactivating one or more Scells.
Further, upon activation of an Scell at the UE, the eNB schedules data transmission over the activated Scell based on a set of parameters such as Channel Quality Information (CQI), Sounding Reference Signal (SRS), Power Head Room (PHR), etc. associated with the activated Scell. However, the set of parameters used for scheduling data transmission may not be up-to-date and usage of outdated parameters may affect performance of the eNB and cause a waste of network resources.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.